Ideal Weight Calculator by Height: Why the Number Changes Between Formulas
Search "ideal weight" and one calculator hands you a single definitive number. Try a different one with the same height and sex, and the number shifts by two or three kilograms. Neither calculator is wrong — "ideal weight" was never a single number to begin with. It's a range produced by several decades-old formulas, each built on slightly different assumptions.
Why do the four formulas disagree?
Devine, Robinson, Miller and Hamwi are four classical formulas developed at different times, all estimating a weight figure mainly from height and sex. Because each was built on different data and assumptions, they don't converge on one number — the gap between them can run to several kilograms for the same height. The ideal weight calculator on Sahel shows the result from all four side by side, along with the gap between them in kilograms, instead of picking one formula and presenting it as the final word.
Seeing all four together is useful precisely because it exposes how much uncertainty sits inside that single number. When the spread between the highest and lowest estimate is two or three kilograms, it becomes clear that "ideal weight" is a range, not a thin line, and that landing inside the range matters more than hitting one exact figure. The calculator also shows the healthy weight range from the WHO BMI bands as an added reference alongside the four formulas.
Body fat — what the four formulas can't tell you
All four formulas rely on height and sex alone, so none of them can distinguish two people at the same weight where one carries more muscle and the other more fat. That's where a body fat estimate comes in: add a few measurements from an ordinary tape measure, using the US Navy method, and the calculator estimates your body fat percentage — the one figure here that actually tells a muscular build apart from a heavier one, unlike the weight number alone, which treats both the same.
That doesn't make the four formulas useless — it just means they serve a different purpose than the body fat estimate. The formulas give you a quick starting point from two things you always know, height and sex, with no tape measure or extra step required. Body fat needs a more careful manual measurement, but it rewards that effort with information no height-based weight formula can offer. Using both together, rather than either one alone, is what gets you closer to an accurate picture.
How to use it
- Enter your height and sex — the two inputs every one of the four formulas needs.
- Check the results from all four formulas, the gap between them in kilograms, and the WHO range shown alongside.
- For body fat, take a tape measure and measure the points the tool asks for carefully — not pulled tight, not left loose.
- Enter those measurements to see an estimated body fat percentage next to the weight range.
- Treat the result as a guide, not a verdict — especially if you carry visible muscle mass.
A real case
A regular weightlifter runs the ideal weight calculator and gets a "target" several kilograms below their actual weight across all four formulas, because none of those formulas separates a kilogram of muscle from a kilogram of fat. Stopping there, they might conclude they're above a healthy weight — which isn't the full picture.
Adding the tape measurement shows a low body fat percentage, consistent with a muscular build rather than excess weight. That gives a clearer picture than the number alone: weight sits above the four-formula range, but the body fat reading says the reason is muscle, not fat. For someone else at the exact same weight with a higher body fat reading, the story told by the same scale number is entirely different.
If both people stopped at the weight number alone, they'd look identical on paper, in a report that ignores the real difference between them. A one-minute tape measurement is enough to reveal that difference, which is exactly what makes pairing the four formulas with a body fat estimate more useful than leaning on either one by itself.
Frequently asked
Which of the four formulas is the most accurate?
None is objectively "more accurate" than the rest — each was built on different assumptions, which is exactly why the calculator shows all four together rather than presenting one as absolute fact. Look at the range they agree on rather than any single figure.
Is a tape-measure body fat estimate as precise as a clinical device?
It's a practical estimate using a tool anyone can access, not a replacement for a specialised medical measurement. Its accuracy depends on how carefully the tape is used, so a consistent measuring technique matters more than any single reading.
Why does my ideal weight number differ from my BMI range?
The four formulas and BMI are different tools using different calculations, so it's normal for their numbers not to match exactly. For a separate comparison based on BMI and its bands, try the BMI calculator.
What if my weight falls outside every range shown?
Falling outside a range isn't a medical verdict — it's a guide worth discussing with a professional if the concern is genuine. This calculator is a wellness tool, not a diagnostic one, and it doesn't replace advice from a qualified professional.
Does the calculator require an account or installation?
No, it runs directly in the browser with no sign-up or install, and it calculates the result as soon as you enter your details.
Try the tool
Open the ideal weight and body fat calculator, enter your height and sex to see all four formula results, then add a tape measurement to estimate body fat in minutes.